It is known in hot- and cold-rolling operations to use a roll formed by a core and a sleeve together defining a chamber that can be pressurized to radially swell the sleeve. In this manner the standard bending of the working rolls can be compensated out, and the hydraulic pressure can be adjusted for different rolling pressures to produce a fairly flat workpiece, as the rolls will be more or less parallel at their confronting surfaces at the rolling nip.
In a standard such arrangement the roll core is dumbbell shaped and is fitted within a cylindrically tubular sleeve. The enlarged ends of the core are radially shrunk by cooling and the sleeve is radially expanded by heating to fit the assembly together, so that when the two parts become the same temperature they are a tight fit. Such a procedure normally axially tensions the sleeve, as it shrinks radially into tight contact with the core ends before it has finished its substantially greater axial shrinking. This of course also axially compresses the core. As a result the roll has a tendency to bend, and this tendency increases when the swelling chamber is pressurized.
Another disadvantage is that a roll of this construction is subjected to substantially more torsion than solid rolls. Such a roll is normally driven from one end of the core only. The reduced diameter central portion of the core cannot transmit the torque from one end to the other without distorting, and the sleeve transmits little torque. The resultant torsional deformation further bends the roll, typically away from the other roll. In hot-rolling operations this torsional deformation is so great that it has a noticeable effect on the workpiece shape, creating the known saber effect, that is the roll edges will be lightly curved but parallel lines, making the strip workpiece difficult to guide in the rolling line.